1. Field of the Invention
The present invention relates, in general, to pneumatically driven dispensers, and, more particularly, to using pressurized gas or air to control the dispensing of a food product.
2. Statement of the Problem
Frozen confections such as ice cream, yogurt, and sorbets are well-liked food items whose popularity has increased in recent years. As their popularity increases, so too does the necessity for dispensing these frozen confections to consumers in measured amounts quickly and easily. It is also desirable to provide a choice of flavors in one location, and to minimize the time needed to clean and refill the dispensers.
A variety of apparatuses have been developed for dispensing frozen confections quickly, easily, and in measured amounts. In general, to dispense a frozen confection, the confection is placed either directly in a receptacle or within a container that is then put in a receptacle. The confection is then forced out of the receptacle by, for example, a piston within the receptacle that is caused to move against the confection or against the collapsible container. The piston thus forces the confection out of an outlet in the receptacle.
Once the confection has been dispensed, it is necessary to retract the piston to clean the receptacle and/or insert additional confection for dispensing. Pistons can be driven by several conventional systems, for example, hydraulics, mechanical engines, or pneumatic systems. Pistons driven by hydraulic or mechanical systems are generally attached to the motive force by a driving shaft that extends from the back of the piston. The piston is both extended and retracted by the driving shaft.
Pistons driven by pneumatics are often "free floating" within their jackets or cylinders. Such free-floating pistons are extended by using pressurized gas to push against the back of the piston.
A search of the prior art in which pressurized gas is used to move a piston to dispense a product out of a receptacle discovered the following patents:
______________________________________ Rowe 5,265,764 Nov. 30, 1993 Beach 5,492,249 Feb. 20, 1996 Gomann 3,327,906 June 27, 1967 Vanderjagt 4,886,189 Dec. 12, 1989 Thomas 5,048,724 Sep. 17, 1991 Thomas 5,405,054 Apr. 11, 1995 Watson 5,114,054 May 19, 1992 McGill 5,150,820 Sept. 29, 1992 Plechinger et al. 5,259,842 Nov. 9, 1993 Danek et al. 5,452,824 Sept. 26, 1995 ______________________________________
U.S. Pat. No. 5,265,764 issued to Rowe sets forth a dual-action free-floating piston within a cylinder. Gas pressure is used to drive the piston to dispense bagged frozen product. After the product is dispensed, the gas pressure is directed to the opposite side of the piston to drive the piston in the opposite direction.
U.S. Pat. No. 5,492,249 to Beach sets forth an apparatus that uses high-pressure air to move a free-floating piston toward the material to be dispensed. A safety device is provided so the apparatus cannot be opened until the air pressure is vented. The operator manually retracts the piston by pushing on it. This patent is assigned to the owner of the present invention.
U.S. Pat. No. 3,327,906 issued to Gomann discloses a piston in a cylinder. The piston is moved by a compressed fluid to dispense a paste contained in the cylinder. A suction generator is used to provide for better sealing of the piston to the cylinder and to remove any compressed fluid that escapes around the sides of the piston.
U.S. Pat. No. 4,886,189 to Vanderjagt teaches an approach for dispensing liquids in which a movable chamber slides down a stationary piston toward the liquid, which is kept in a separate chamber. Either air pressure or vacuum is used to move the chamber.
U.S. Pat. Nos. 5,048,724 and 5,405,054 to Thomas disclose a confection dispenser in which a collapsible container holding the confection is compressed in order to extrude the confection from the dispenser. Preferably, a bellows is used that is caused to expand by admitting pressurized air into the interior of the bellows. The expanding bellows pushes against the collapsible container. To replace the collapsible container, the air pressure inside the expanded bellows is released either automatically or manually.
U.S. Pat. No. 5,114,054 to Watson teaches a piston in a tank in which the piston is moved by air pressure.
U.S. Pat. No. 5,150,820 to McGill teaches a frozen product-dispensing apparatus in which a cylindrical deformable container holds the products. The container is compressed by a plunger that is moved by compressed air. The compressed air is applied either directly to the plunger or to a bellows that engages the plunger.
U.S. Pat. No. 5,259,842 to Plechinger et al. discloses a high-pressure liquid dispenser containing a pump piston. The pump piston is driven by a fluid-actuated drive.
U.S. Pat. No. 5,452,824 to Danek et al. teaches a syringe for automatically dispensing fluid dots. The plunger of the syringe is displaced by pressurized air.
The pistons can be retracted in several ways. In one way, as shown in the Rowe patent, the pressurized air is routed to the front of the piston to push it back. This system necessitates providing several apertures and more than one sealed pressure chamber. Frost, spilled product, and the product container itself may create a hindrance to sealing around the door at the dispensing end of the dispensing cylinder.
In another method of retraction, as for the Beach system, the piston is retracted manually by pushing against the product side of the piston by hand or with a rod after the pressurized air is released. This method may expose the operator's garments and skin to lubricants used for the piston and to spilled product, thus soiling the operator's clothing. Another, potentially greater, negative aspect of this method is that great force (up to 100 lbf) may be required to push the piston back to its fully retracted position so that new product may be placed in the dispensing cylinder. Such great force may be required due to either lack of lubrication between the piston and the cylinder walls or the build-up of frost behind the piston resulting from chilling of the compressed air used to move the piston forward. Thus, a need exists to automate the release of pressurized gas and retraction of the piston without additional apertures or sealed pressure chambers.
Yet another method by which the piston may be retracted would be the use of a mechanical device to pull the piston back, such as a metal coil compression spring, elastic band (for example, surgical tubing), or a coil spring reel with a cable located within the cylinder connecting the bottom cap of the cylinder to the piston. All these options would occupy space in the cylinder and prevent the piston from contacting the bottom cap, thus requiring a longer cylinder to dispense a product container of fixed length. If any of these mechanical devices should break, the dispensing cylinder assembly will require disassembly to repair or replace the device. In addition, frost and ice build-up may prohibit the device from functioning or may increase the force required to move the piston to a quantity greater that that produced by the device. Many elastomeric materials often become rigid and lose their elastic properties when placed in a cold environment. Any of the previous listed mechanical devices would automatically pull the piston toward the bottom cap when gas pressure is released from the dispensing cylinder (for example, during a door opening to check product levels). This may cause a partially full product container to stretch back with the piston and cause a situation in which the product container may fold upon itself, thus blocking the flow of product.
Yet another difficulty frequently encountered is the freezing of an empty container to the top of the dispensing piston. A receptacle is often incorporated into the dispensing side of the piston for receiving and managing the collapsed container. The collapsed container often becomes adhered to the receptacle, requiring great force (more than 50 lbf) to remove. Thus, a need exists to provide variable force using the same source of pressurized air or gas without additional apertures or sealed pressure chambers.
The use of pressurized gas to move the piston presents additional problems. First, and most important, it is necessary to provide for a method to release the pressurized gas from the dispenser when the piston is not moving or when the dispenser is opened. This release of the pressurized gas prevents injury to operators should the dispenser be opened inadvertently. It is further desirable to release the gas as fast as possible so that the downtime in which no product is dispensed is minimized. Finally, it is desirable to release the pressurized gas without making any additional apertures in the dispenser.
None of the dispensing systems described above provides a method for pneumatically retracting a piston by supplying a pneumatic gas source to the same side of the piston that is used when extending the piston, using the same aperture and the same sealed pressure chamber. Neither do any of the dispensing systems described above provide a system having three automatic modes of operation: a dispensing mode, a retraction mode, and a resting or exhaust mode.